In 3GPP Long Term Evolution (LTE) systems, multi-user multiple-input multiple output (MU-MIMO) data transmissions can be used to send data from an evolved Node B (eNB) to more than one wireless transmit/receive unit (WTRU) over the same set of time/frequency resources. In order for a WTRU to properly receive this data, it must configure itself according to a set of transmission parameters which are sent by the eNB using a pre-defined downlink control format. The downlink control information (DCI) format to be used by the eNB to signal these parameters is undecided.
Current signaling for MU-MIMO parameters consist of signaling parameters using DCI format 1D. MU-MIMO DCI format 1D is based on DCI format 1B, which is used for single codeword rank 1 precoding SU-MIMO, with potential modification/reinterpretation of specific bits. In one method for signaling transmit power sharing information that maintains the DCI format 1B signal format size, transmit power sharing is indicated using one bit. In the 2 transmitting antennas (2Tx) and 4 transmitting antennas (4Tx) cases, the distributed virtual resource block (DVRB) flag of DCI format 1B is reused to implement a two level power offset. In this scheme, a power offset value of 0 represents a −3 dB decrease with respect to the single user transmission (Tx) power offset signaled by higher layers and a power offset value of 1 represents the same level as the single user transmitting antenna power offset signaled by higher layers. All other fields are the same as in DCI format 1B. The reuse of the DVRB flag removes the option of using DVRBs in order to signal the power sharing ratio.
Alternatives to the above methods have been proposed. A first option reintroduced the DVRB flag and therefore the option of having DVRBs. This kept the two level power offset and maintained a signal format size equal to DCI format 1B for both 2Tx and 4Tx transmissions. A second option didn't reintroduce the DVRB flag and used a four level power offset for the 4Tx case. This second option led to a smaller signal format size than DCI format 1B for the 2Tx case and the same size for the 4Tx case. A third option reintroduced the DVRB flag and used a four level power offset for the 4Tx case. This option maintained a signal format size equal to DCI format 1B for the 2Tx case and a larger signal format size than DCI format 1B for the 4Tx case.
These options have issues including limiting power sharing to two WTRUs, and signal format size not equal to DCI format 1B. The argument for having the same size for DCI formats 1B and 1D is that only one performance test needs to be done rather than two. Therefore methods are needed for signaling parameters to a WTRU that support proper reception of MU-MIMO data transmissions from the eNB including support for four co-scheduled WTRUs for eNBs having four transmit antennas and maintaining a predetermined signal format size.